| 1 | /* Copyright (C) 2005-2022 Free Software Foundation, Inc. |
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| 2 | This file is part of the GNU C Library. |
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| 3 | |
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| 4 | The GNU C Library is free software; you can redistribute it and/or |
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| 5 | modify it under the terms of the GNU Lesser General Public |
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| 6 | License as published by the Free Software Foundation; either |
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| 7 | version 2.1 of the License, or (at your option) any later version. |
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| 8 | |
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| 9 | The GNU C Library is distributed in the hope that it will be useful, |
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 12 | Lesser General Public License for more details. |
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| 13 | |
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| 14 | You should have received a copy of the GNU Lesser General Public |
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| 15 | License along with the GNU C Library. If not, see |
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| 16 | <https://www.gnu.org/licenses/>. */ |
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| 17 | |
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| 18 | #include "pthreadP.h" |
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| 19 | #include <shlib-compat.h> |
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| 20 | |
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| 21 | int |
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| 22 | __pthread_spin_unlock (pthread_spinlock_t *lock) |
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| 23 | { |
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| 24 | /* CONCURRENCTY NOTES: |
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| 25 | |
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| 26 | The atomic_exchange_rel synchronizes-with the atomic_exhange_acq in |
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| 27 | pthread_spin_lock. |
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| 28 | |
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| 29 | On hppa we must not use a plain `stw` to reset the guard lock. This |
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| 30 | has to do with the kernel compare-and-swap helper that is used to |
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| 31 | implement all of the atomic operations. |
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| 32 | |
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| 33 | The kernel CAS helper uses its own internal locks and that means that |
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| 34 | to create a true happens-before relationship between any two threads, |
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| 35 | the second thread must observe the internal lock having a value of 0 |
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| 36 | (it must attempt to take the lock with ldcw). This creates the |
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| 37 | ordering required for a second thread to observe the effects of the |
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| 38 | RMW of the kernel CAS helper in any other thread. |
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| 39 | |
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| 40 | Therefore if a variable is used in an atomic macro it must always be |
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| 41 | manipulated with atomic macros in order for memory ordering rules to |
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| 42 | be preserved. */ |
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| 43 | atomic_exchange_rel (lock, 0); |
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| 44 | return 0; |
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| 45 | } |
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| 46 | versioned_symbol (libc, __pthread_spin_unlock, pthread_spin_unlock, |
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| 47 | GLIBC_2_34); |
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| 48 | |
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| 49 | #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_2, GLIBC_2_34) |
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| 50 | compat_symbol (libpthread, __pthread_spin_unlock, pthread_spin_unlock, |
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| 51 | GLIBC_2_2); |
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| 52 | #endif |
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| 53 | |
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